Somewhere around age 40 my wife's libido took a spiral dive. When her ob/gyn suggested there may be ways to revive her interest she changed doctors. I still remember the last time she initiated sex, about 1992.
But what was the real defining moment. When I came home from a business trip and found her toys on the night stand, that would have been in 2008 or 9. So she would still masturbate but found no pleasure in intercourse.
On the enema side, for the first 5 years of our marriage, when we started dating I told all, she tried them and loved them, then one day it was, I'm not doing this anymore. But she would still give them to me, until one day, after saying she felt superfluous, then that stopped.
My wife worked in an all male environment as a machinist, aircraft mechanic and locomotive engineer. I've often wondered if she had worked with women or a mix of men and women if that would have made a difference. She was well respected by her coworkers, and one of the boys. No kids, two tubal pregnancies took that off the table, so I have wondered if that was a factor. Atheist, pro-choice, gay rights, liberal, traits we shared, so no issues there. But no "you have to submit to your husband" religious issues, maybe I would have been off with a Mormon!.